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Zhao 4 Updates: 6550,8138 (if approved) Cisco Systems 5 Intended status: Standards Track May 29, 2019 6 Expires: November 30, 2019 8 Configuration option for RFC 8138 9 draft-thubert-roll-turnon-rfc8138-01 11 Abstract 13 This document complements RFC 8138 and dedicates a bit in the RPL 14 configuration option defined in RFC 6550 to indicate whether RFC 8138 15 compression is used within the RPL instance. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on November 30, 2019. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 53 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 2 54 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3 55 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 3 56 5.1. Inconsistent State While Migrating . . . . . . . . . . . 4 57 5.2. Single Instance Scenario . . . . . . . . . . . . . . . . 5 58 5.3. Double Instance Scenario . . . . . . . . . . . . . . . . 5 59 5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 61 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 62 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 63 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 64 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 65 9.2. Informative References . . . . . . . . . . . . . . . . . 7 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 68 1. Introduction 70 The transition to [RFC8138] in a network can only be done when all 71 nodes support the specification. In a mixed case with both 72 RFC8138-capable and non-capable nodes, the compression should be 73 turned off. 75 This document complements RFC 8138 and dedicates a bit in the RPL 76 configuration option to indicate whether RFC 8138 compression should 77 be used within the RPL instance. When the bit is not set, source 78 nodes that support RFC 8138 should refrain from using the compression 79 unless the information is superseded by configuration. 81 2. BCP 14 83 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 84 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 85 "OPTIONAL" in this document are to be interpreted as described in BCP 86 14 [RFC2119][RFC8174] when, and only when, they appear in all 87 capitals, as shown here. 89 3. Updating RFC 6550 91 RPL defines a configuration option that is registered to IANA in 92 section 20.14. of [RFC6550]. This specification defines a new flag 93 "Enable RFC8138 Compression" (T) that is encoded in one of the 94 reserved control bits in the option. The new flag is set to turn on 95 the use of the compression of RPL artifacts with RFC 8138. 97 4. Updating RFC 8138 99 This document specifies controls that enable and disable the use of 100 the [RFC8138] compression in a RPL Instance. Arguably, this could 101 have been done in [RFC8138] itself. 103 A node that supports this specification SHOULD source packets in the 104 compressed form using [RFC8138] if the new "T" flag is set in the RPL 105 configuration option from its parents. Failure to do so will result 106 in larger packets, yields higher risks of loss and may cause a 107 fragmentation. 109 A node that supports this specification SHOULD refrain from sourcing 110 packets in the compressed form using [RFC8138] if the "T" flag is 111 reset. This behaviour can be overridden by a configuration of the 112 node in order to cope with intermediate implementations of the root 113 that support [RFC8138] but not this specification and cannot set the 114 "T" flag. 116 The decision of using RFC 8138 to compress a packet is made at the 117 source depending on its capabilities and its knowledge of the state 118 of the "T" flag. A router MUST forward the packet in the form that 119 the source used, either compressed or uncompressed. A router that 120 encapsulates a packet is the source of the resulting packet and the 121 rules above apply to it in that case. 123 5. Transition Scenarios 125 A node that supports [RFC8138] but not this specification can only be 126 used in an homogeneous network and an upgrade requires a "flag day" 127 where all nodes are updated and then the network is rebooted with 128 implicitely RFC 8138 compression turned on with the "T" flag set on. 130 A node that supports this specification can work in a network with 131 RFC 8138 compression turned on or off with the "T" flag set 132 accordingly and in a network in transition from off to on or on to 133 off (see Section 5.1). 135 A node that does not support [RFC8138] can interoperate with a node 136 that supports this specification in a network with RFC 8138 137 compression turned off. But it cannot forward compressed packets and 138 therefore it cannot act as a router in a network with RFC 8138 139 compression turned on. It may remain connected to that network as a 140 leaf and generate uncompressed packets as long as imcomping packets 141 are decapsulated by the parent and delivered in uncompressed form. 143 [RFC6550] states that "Nodes other than the DODAG root MUST NOT 144 modify this information when propagating the DODAG Configuration 145 option". In other words, the configuration option is a way for the 146 root to configure the LLN nodes but it cannot be used by a parent to 147 advertise its capabilities down the DODAG. It results whether a 148 parent supportqs RFC 8138 is not known by the child with the current 149 level of specifications, and a child cannot favor a parent based on a 150 particular support. 152 [RFC6550] also suggests that a RPL node may attach to a DODAG as a 153 leaf node only, e.g., when a node does not support the RPL Instance's 154 Objective Function (OF) as indicated by the Objective Code Point 155 (OCP) in the configuration option. But the node is also free to 156 refrain from joining an Instance when a parameter is not suitable. 157 This means that changing the OCP in a DODAG can be used to force 158 nodes that do not support a particular feature to join as leaf only, 159 but the method is not guaranteed to work with all implementations. 160 With this specification, it is now RECOMMENDED that a node that is 161 configured to operate in an Instance but does not recognize a 162 parameter that is mandatory for routing still joins as a leaf. 164 The intent for this specification is to perform a migration once and 165 for all wihtout the need for a flag day. In particular it is not the 166 intention to undo the setting of the "T" flag, and though it is 167 possible to roll back (see Section 5.4), adding nodes that do not 168 support [RFC8138] after a roll back may be problematic if the roll 169 back is not fully complete (see caveats in Section 5.2). 171 5.1. Inconsistent State While Migrating 173 When the 'T' flag is turned on in the configuration option by the 174 root, the information slowly percolates through the DODAG as the DIO 175 gets propagated. Some nodes will see the flag and start sourcing 176 packets in the compressed form while other nodes in the same instance 177 are still not aware of it. Conversely, in non-storing mode, the root 178 will start using RFC 8138 with a SRH-6LoRH that routes all the way to 179 the last router or to the leaf, depending on its support. 181 This is why it is required that all the routers in the Instance 182 support [RFC8138] at the time of the switch, and all nodes that do 183 not support [RFC8138] only operate as leaves. 185 Setting the "T" flag is ultimately the responsibility of the network 186 administrator. In a case of upgrading a network to turn the 187 compression on, the network SHOULD be operated with the "T" flag 188 reset until all targeted nodes are upgraded to support this 189 specification. Section 5.2 and Section 5.3 provide possible 190 transition scenarios where this can be enforced. 192 5.2. Single Instance Scenario 194 In a single instance scenario, nodes that support RFC 8138 are 195 configured with a new OCP, that may use the same OF operation or a 196 variation of it. when it finally sets the "T" flag, the root also 197 migrates to the new OCP. As a result, nodes that do not support RFC 198 8138 join as leaves and do not forward packets anymore. The leaves 199 generate packets without compression. The parents - which supports 200 RFC 8138 - may encapsulate the packets using RFC 8138 if needed. The 201 other way around, the root encapsulates packets to the leaves all the 202 way to the parent, which decapsulates and distribute the uncompresses 203 inner packet to the leaf. 205 This scenario presents a number of caveats: 207 o The method consumes an extra OCP. It also requires a means to 208 signal the capabilities of the leaf, e.g., using "RPL Mode of 209 Operation extension" [I-D.rahul-roll-mop-ext]. 211 o If an implementation does not move to a leaf mode when the OCP is 212 changed to an unknown one, then the node may be stalled. 214 o If the only possible parents of a node are nodes that do not 215 support RFC 8138, then that node will loose all its parent at the 216 time of the migration and it will be stalled until a parent is 217 deployed with the new capability. 219 o Nodes that only support RFC8138 for forwarding may not parse the 220 RPI in native form. If such nodes are present, the parent needs 221 to encapsulate with RFC8138. 223 5.3. Double Instance Scenario 225 An alternate to the Single Instance Scenario is to deploy an 226 additional Instance for the nodes that support [RFC8138]. The two 227 instances operate as ships-in-the-night as specified in [RFC6550]. 228 The preexisting Instance that does not use [RFC8138], whereas the new 229 Instance does. This is signaled by the "T" flag which is only set in 230 the configuration option in DIO messages in the new Instance. 232 Nodes that support RFC 8138 participate to both Instances but favor 233 the new Instance for the traffic that they source. On the other 234 hand, nodes that only support the uncompressed format would either 235 not be configured for the new instance, or would be configured to 236 join it as leaves only. 238 This method eliminates the risks of nodes being stalled that are 239 described in Section 5.2 but requires implementations to support at 240 least two RPL Instances and demands mamangement capabilities to 241 introduce new Instances and deprecate old ones. 243 5.4. Rolling Back 245 After downgrading a network to turn the [RFC8138] compression off, 246 the administrator SHOULD make sure that all nodes have converged to 247 the to the "T" flag reset before allowing nodes that do not support 248 [RFC8138] in the network (see caveats in Section 5.2). 250 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 251 network where the compression is turned on. A node that does not 252 support [RFC8138] MUST be used only as a leaf. 254 6. IANA Considerations 256 This specification updates the "Registry for the DODAG Configuration 257 Option Flags" that was created for [RFC6550] as follows: 259 +---------------+---------------------------------+----------------+ 260 | Bit Number | Meaning | Defining Spec | 261 +---------------+---------------------------------+----------------+ 262 | 2 (suggested) | Turn on RFC8138 Compression (T) | This | 263 +---------------+---------------------------------+----------------+ 265 Table 1: New DODAG Configuration Option Flag 267 7. Security Considerations 269 No specific threat was identified with this specification. 271 8. Acknowledgments 273 9. References 275 9.1. Normative References 277 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 278 Requirement Levels", BCP 14, RFC 2119, 279 DOI 10.17487/RFC2119, March 1997, 280 . 282 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 283 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 284 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 285 Low-Power and Lossy Networks", RFC 6550, 286 DOI 10.17487/RFC6550, March 2012, 287 . 289 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 290 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 291 May 2017, . 293 9.2. Informative References 295 [I-D.rahul-roll-mop-ext] 296 Jadhav, R. and P. Thubert, "RPL Mode of Operation 297 extension", draft-rahul-roll-mop-ext-00 (work in 298 progress), February 2019. 300 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 301 "IPv6 over Low-Power Wireless Personal Area Network 302 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 303 April 2017, . 305 Authors' Addresses 307 Pascal Thubert (editor) 308 Cisco Systems, Inc 309 Building D 310 45 Allee des Ormes - BP1200 311 MOUGINS - Sophia Antipolis 06254 312 FRANCE 314 Phone: +33 497 23 26 34 315 Email: pthubert@cisco.com 317 Li Zhao 318 Cisco Systems, Inc 319 Xinsi Building 320 No. 926 Yi Shan Rd 321 SHANGHAI 200233 322 CHINA 324 Email: liz3@cisco.com